rearing

Beetle Collecting 101: How to rear wood-boring beetles

/ Ted C. MacRae / 13 Comments

I’ve been collecting wood-boring beetles for more than three decades now, and if I had to make a list of “essential” methods for collecting them I would include “beating,” “blacklighting,” and “rearing.” Beating is relatively straightforward—take a beating sheet (a square piece of cloth measuring 3–5 ft across and suspended beneath wooden, metal, or plastic cross members), position it beneath a branch of a suspected host plant, and tap the branch with a stick or net handle. Many wood-boring beetles tend to hang out on branches of their host plants, especially recently dead ones, and will fall onto the sheet when the branch is tapped. Be quick—some species (especially jewel beetles in the genus Chrysobothris) can zip away in a flash before you have a chance to grab them (especially in the heat of the day). Others (e.g., some Cerambycidae) may remain motionless and are cryptically colored enough to avoid detection among the pieces of bark and debris that also fall onto the sheet with them. Nevertheless, persistence is the key, and with a little practice one can become quite expert at efficiently collecting wood-boring beetles using this method. Blacklighting is even easier—find the right habitat (preferably on a warm, humid, moonless night), set up a blacklight in front of a white sheet, crack open a brew, and wait for the beetles to come!

Rearing, on the other hand, takes true dedication. One must not only learn potential host plants, but also how to recognize wood with the greatest potential for harboring larvae, retrieve it from the field, cut it up, place it in rearing containers, and monitor the containers for up to several months or even years before hitting pay dirt (maybe!). Despite the considerable amount of effort this can take, the results are well worth it in terms of obtaining a diversity of species (usually in good series), some of which may be difficult to encounter in the field, and identifying unequivocal larval host associations. I have even discovered two new species through rearing (Bellamy 2002, MacRae 2003)! Moreover, checking rearing containers can be a lot of fun—in one afternoon you can collect dozens or even hundreds of specimens from places far and wide, depending on how far you are willing to travel to collect the wood. Because of the effort involved, however, the more you can do to ensure that effort isn’t wasted on uninfested wood and that suitable conditions are provided to encourage continued larval development and adult emergence from infested wood the better. It is with this in mind that I offer these tips for those who might be interested in using rearing as a technique for collecting these beetles.

I should first clarify what I mean by “wood-boring” beetles. In the broadest sense this can include beetles from any number of families in which the larvae are “xylophagous,” i.e., they feed within dead wood. However, I am most interested in jewel beetles (family Buprestidae) and longhorned beetles (family Cerambycidae), and as a result most of the advice that I offer below is tailored to species in these two families. That is not to say that I’ll turn down any checkered beetles (Cleridae), powderpost beetles (Bostrichidae), bark beetles (family Scolytidae), or even flat bark beetles sensu lato (Cucujoidea) that I also happen to encounter in my rearing containers, with the first two groups in particular having appeared in quite good numbers and diversity in my containers over the years. Nevertheless, I can’t claim that my methods have been optimized specifically for collecting species in these other families.

First, you have to find the wood. In my experience, the best time to collect wood for rearing is late winter through early spring. A majority of species across much of North America tend to emerge as adults during mid- to late spring, and collecting wood just before anticipated adult emergence allows the beetles to experience natural thermoperiods and moisture regimes for nearly the duration of their larval and pupal development periods. Evidence of larval infestation is also easier to spot once they’ve had time to develop. That said, there is no “bad” time to collect wood, and almost every time I go into the field I am on the lookout for infested wood regardless of the time of year. The tricky part is knowing where to put your efforts—not all species of trees are equally likely to host wood-boring beetles. In general, oaks (Quercus), hickories (Carya), and hackberries (Celtis) in the eastern U.S. host a good diversity of species, while trees such as maples (Acer), elms (Ulmus), locust (Gleditsia and Robinia), and others host a more limited but still interesting fauna. In the southwestern U.S. mesquite (Prosopis) and acacia (Acacia) are highly favored host plants, while in the mountains oaks are again favored. Everywhere, conifers (Pinus, Abies, Juniperus, Tsuga, etc.) harbor a tremendous diversity of wood-boring beetles. To become good at rearing wood-boring beetles, you have to become a good botanist and learn not only how to identify trees, but dead wood from them based on characters other than their leaves! Study one of the many good references available (e.g., Lingafelter 2007, Nelson et al. 2008) to see what the range of preferred host plants are and then start looking.

I wish it were as simple as finding the desired types of trees and picking up whatever dead wood you can findm but it’s not. You still need to determine whether the wood is actually infested. Any habitat supporting populations of wood-boring beetles is likely to have a lot of dead wood. However, most of the wood you find will not have any beetles in it because it is already “too old.” This is especially true in the desert southwest, where dead wood can persist for very long periods of time due to low moisture availability. Wood-boring beetles begin their lives as eggs laid on the bark of freshly killed or declining wood and spend much of their lives as small larvae that are difficult to detect and leave no obvious outward signs of their presence within or under the bark. By the time external signs of infestation (e.g., exit holes, sloughed bark exposing larval galleries, etc.) become obvious it is often too late—everything has already emerged. Instead, look for branches that are freshly dead that show few or no outward signs of infestation. You can slice into the bark with a knife to look for evidence of larval tunnels—in general those of longhorned beetles will be clean, while those of jewel beetles will be filled with fine sawdust-like frass that the larva packs behind it as it tunnels through the wood. Oftentimes the tunnels and larvae will be just under the bark, but in other cases they may be deeper in the wood. Broken branches hanging from live trees or old, declining trees exhibiting branch dieback seem to be especially attractive to wood-boring beetles, while dead branches laying on the ground underneath a tree are not always productive (unless they have been recently cut).

One way to target specific beetles species is to selectively cut targeted plant species during late winter, allow the cut branches to remain in situ for a full season, and then retrieve them the following winter or early spring. These almost always produce well. Doing this will also give you a chance to learn how to recognize young, infested wood at a time that is perfect for retrieval, which you can then use in searching for wood from other tree species in the area that you may not have had a chance to cut. I have cut and collected branches ranging from small twigs only ¼” diameter to tree trunks 16″ in diameter. Different species prefer different sizes and parts of the plant, but in general I’ve had the best luck with branches measuring 1–3″ diameter.

Once you retrieve the wood, you will need to cut it into lengths that fit into the container of your choice (a small chain saw makes this much easier and quicker). In the field I bundle the wood with twine and use pink flagging tape to record the locality/date identification code using a permanent marker. I then stack the bundles in my vehicle for transport back home. Choice of container is important, because moisture management is the biggest obstacle to rearing from dead wood—too much moisture results in mold, while too little can lead to desiccation. Both conditions can result in mortality of the larvae or unemerged adults. In my rearing setup, I use fiber drums ranging from 10-G to 50-G in size (I accumulated them from the dumpster where I work—mostly fiber drums used as shipping containers for bulk powders). Fiber drums are ideal because they not only breath moisture but are sturdy and may be conveniently stacked. Cardboard boxes also work as long as they are sturdy enough and care is taken to seal over cracks with duct tape. Avoid using plastic containers such as 5-G pickle buckets unless you are willing to cut ventilation holes and hot-glue fine mesh over them. While breathable containers usually mitigate problems with too much moisture, desiccation can still be a problem. To manage this, remove wood from containers sometime later in the summer (after most emergence has subsided), lay it out on a flat surface such as a driveway, and hose it down real good. Once the wood has dried sufficiently it can be placed back in the container; however, make sure the wood is completely dry or this will result in a flush of mold. I generally also wet down wood again in late winter or early spring, since I tend to hold wood batches through two full seasons.

I like to check containers every 7–15 days during spring and summer. Some people cut a hole in the side of the container that leads into a clear jar or vial—the idea being that daylight will attract newly emerged adults and facilitate their collection. I’ve tried this and was disappointed in the results—some of the beetles ended up in the vial, but many also never found their way to the vial and ended up dying in the container, only to be found later when I eventually opened it up. This is especially true for cerambycids, many of which are nocturnal and thus probably not attracted to daylight to begin with. My preference is to open up the container each time so that I can check the condition of the wood and look for evidence of larval activity (freshly ejected frass on the branches and floor of the container). I like to give the container a ‘rap’ on the floor to dislodge adults from the branches on which they are sitting, then dump the container contents onto an elevated surface where I can search over the branches and through the debris carefully so as not to miss any small or dead specimens. I use racks of 4-dram vials with tissue packed inside each and a paper label stuck on top of its polypropylene-lined cap as miniature killing jars. Specimens from a single container are placed in a vial with a few drops of ethyl acetate, and I write the container number and emergence date range on the cap label. Specimens will keep in this manner until they are ready to be mounted weeks or months (or even years) later. If the vial dries out, a few drops of ethyl acetate and a few drops of water followed by sitting overnight is usually enough to relax the specimens fully (the water relaxes the specimens, and the ethyl acetate prevents mold if they need to sit for a while longer).

I store my containers in an unheated garage that is exposed to average outdoor temperatures but probably does not experience the extreme high and low temperatures that are experienced outdoors. In the past I wondered if I needed more heat for wood collected in the desert southwest, but I never came up with a method of exposing the containers to the sun without also having to protect them from the rain. Metal or plastic containers might have eliminated this problem, but then breathability would again become an issue. I would also be concerned about having direct sun shining on the containers and causing excessive heat buildup inside the bucket that could kill the beetles within them. Now, however, considering the success that I’ve had in rearing beetles from wood collected across the desert southwest—from Brownsville, Texas to Jacumba, California, this seems not to be a big issue.

If anybody else has tips for rearing wood-boring beetles that they can offer, I would love to hear from you.

REFERENCES:

Bellamy, C. L. 2002. The Mastogenius Solier, 1849 of North America (Coleoptera: Buprestidae: Polycestinae: Haplostethini). Zootaxa 110:1–12 [abstract].

Lingafelter, S. W. 2007. Illustrated Key to the Longhorned Woodboring Beetles of the Eastern United States. Special Publication No. 3. The Coleopterists Society, North Potomac, Maryland, 206 pp. [description].

MacRae, T. C. 2003. Agrilus (s. str.) betulanigrae MacRae (Coleoptera: Buprestidae: Agrilini), a new species from North America, with comments on subgeneric placement and a key to the otiosus species-group in North America. Zootaxa 380:1–9 [pdf].

Nelson, G. H., G. C. Walters, Jr., R. D. Haines, & C. L. Bellamy.  2008.  A Catalogue and Bibliography of the Buprestoidea of American North of Mexico.  Special Publication No. 4. The Coleopterists Society, North Potomac, Maryland, 274 pp. [description].

Copyright © Ted C. MacRae 2014

Isn’t she splendid?!

/ Ted C. MacRae / 15 Comments

Cicindela splendida | Bald Hill Glade Natural Area, Ripley Co., Missouri

This gorgeous female Cicindela splendida emerged recently from one of my rearing containers.  She was one of several 3rd instar larvae that I collected this past June from their burrows in a dolomite glade in southeastern Missouri.  I had suspected they might represent this species because of the bright, metallic sheen on their heads and decided to rear them out to find out for sure.  Rearing tiger beetles is fun and easy—all you have to do is fill a container with native soil, make a “starter” burrow¹ and drop them in. In this case, I also partially sunk a native rock into the soil in the center of the container, something I have started doing recently as it gives the emerged adult an elevated and more visually appealing surface on which to perch than the soil should I desire to take photographs.

¹ Larvae will dig new burrows on their own, but starter burrows allow you to place the burrow where you want it.  They are essential if more than one larva is introduced to the container, as wandering larvae will fight when they encounter each other. I like to start the burrow in a corner of the container (a pencil works great for this) and push down to the bottom of the container so I can see into the burrow from outside to monitor the larva as it develops.  After introducing the larva to its burrow, I push the soil around the entrance to seal it lightly to keep the larva from immediately crawling back out.  The larva will eventually reopen the burrow but generally accepts it, digging it out further to its liking and shaping the entrance to precisely fit the size and shape of its head.

Reared from 3rd instar larva, burrow in sparsely vegetated clay exposure of dolomite glade.

With tiger beetle rearing, feeding time is fun time! Our lab rears insects for testing in abundance, and there are always leftovers. Really just about any insect that can be pulled into the burrow will be acceptable as prey, but lepidopteran caterpillars are my favorite. I use mostly early instar tobacco hornworm larvae, choosing the size as appropriate for the size of the tiger beetle larva—the big ones (e.g. 3rd instar Tetracha) can handle caterpillars 35-40 mm in length and 6-8 mm in diameter, while neonates must be used for the smallest ones (e.g. 1st instar Cylindera celeripes and C. cursitans). I find it endlessly entertaining to sneak up on the larva sitting at the entrance of its burrow, slowly position a caterpillar above the burrow entrance with forceps, and dangle it to entice the tiger beetle larva to lurch out, grab the caterpillar, and drag it down into its burrow—all in a split second! If the larva drops down from the burrow entrance during my approach I just drop the caterpillar into the burrow (though this isn’t nearly as much fun).

Copyright © Ted C. MacRae 2011

Sugarcane Weevil in Brazil

/ Ted C. MacRae / 2 Comments

Sphenophorus levis (sugarcane weevil) | Conchal, Brazil.

Brazil is one of the world’s top producers of sugarcane, and they have the Middle East to thank for it.  While the U.S. was responding to the 1973 OPEC oil embargo by building bigger and bigger SUVs, Brazil aggressively developed an alternative fuels industry based on sugarcane for ethanol production.  Today, about half of Brazil’s sugarcane is milled for ethanol, yet despite this enough raw sugar is produced from the remaining sugarcane crop to rival India as the world’s top producer.

The large acreage devoted to sugarcane and tropical climate in which it is grown make Brazil’s crop especially vulnerable to infestation by insect pests—and there are many!  One of the most important is Sphenophorus levis (sugarcane weevil, or “bicudo da cana-de-açúcar”).  Larvae bore in the roots and crown of the plant, reducing biomass accumulation and longevity.  This feature of the insect’s biology also makes the larvae extraordinarily difficult to control, since they are largely protected from chemical applications by surrounding plant tissues.  This adult beetle was captured in a field trap placed in a sugarcane field in Conchal, approximately 175 km N of São Paulo.  The traps consist of split sugarcane stalks buried under debris within crop rows—adults are attracted to the cut surface of the stalks, where they congregate in numbers.  Traps are used not only to monitor beetle occurrence and abundance in fields, but also to provide a source of insects for laboratory rearing and evaluation of control test agents.

Copyright © Ted C. MacRae 2011

Rearing the Prairie Tiger Beetle (Cicindela obsoleta vulturina)

/ Ted C. MacRae / 12 Comments

A Prairie Tiger Beetle larva peers up from its burrow in rocky soil of a dolomite glade in the White River Hills of southwestern Missouri. The head of this 3rd-instar larvae is about the size of a pencil eraser.

I had so looked forward to the long Memorial Day weekend collecting trip – time of season and the weather were perfect, and it had been several years since I’d made a late spring swing through the woodlands, glades, and prairies of western Missouri. But after two fruitless days of searching for nearly non-existent beetles at Ha Ha Tonka State Park, Lichen Glade Natural Area, and Penn-Sylvania Prairie, I was faced with a choice: return home disappointed or try something completely different in an attempt to salvage the weekend.  I chose the latter.

A 3rd-instar Prairie Tiger Beetle larva extracted from its burrow. Total length is ~30mm.

What could be more different than the White River Hills of southwestern Missouri?  The deeply dissected dolomite bedrocks supporting xeric, calcareous glades, dry woodlands and riparian watercourses couldn’t be more different than the gentle, acidic sandstone terrain of those more northerly locations.  Its hilltop glades (“balds”) are the most extensive such system in Missouri, and I’ve already featured several charismatic insects from my travels last summer to this part of Missouri, including Megaphasma denticrus (North America’s longest insect), Microstylus morosum (North America’s largest robber fly), and Plinthocoelium suaveolens (North America’s most beautiful longhorned beetle).  One insect that I also wanted to feature from that area but that eluded me during last fall’s cold and wet collecting trip is the Prairie Tiger Beetle – Cicindela obsoleta vulturina.  This impressive species is highly localized in Missouri, occurring no further north and east than the White River Hills.  Moreover, the populations in this part of the state and across the border in Arkansas are highly disjunct from the species’ main population in the southern Great Plains.  Like a number of other plants and animals, the Missouri/Arkansas disjunct may represent a relict from the hypsithermal maximum of several thousand years ago, finding refuge in these rocky hills after cooling temperatures and increasing moisture caused the grasslands of today’s west to retreat from their former eastern extent.

The ''business end'' - four eyes and two enormous mandibles. The metallic purple pronotum is covered with soil.

Despite its restricted occurrence in Missouri, the species is apparently secure and occurs commonly on the many dolomite glades that are found in the area. I have records from a number of localities in the White River Hills, but the best populations I’ve seen occur at Blackjack Knob in Taney County.  Of course, I would have absolutely no chance of seeing the adults during this Memorial Day weekend – adults don’t come out until late summer rains trigger emergence in late August and early September.  It was not, however, the adults that I was after, for I had seen larvae of what I believed must be this species in their burrows during one of my visits to this location last summer.  Although I have collected several other species of tiger beetles in the area, I reasoned these larvae must represent C. obsoleta vulturina due to their rather large size (this species is one of the largest in the genus in North America) and because they lacked the white bordering of the pronotum typical of species in the genus Tetracha – the only other genus occurring in Missouri with species as large as this.  I had tried to extract some of the larvae for an attempt at rearing, but neither of the two techniques I tried (“fishing” and “jabbing”) had worked.  Fishing involves inserting a thin grass stem into the burrow and yanking out the larva when it bites the stem; however, I found the burrows of this species to angle and turn due to the rocky soil rather than go straight down for a clear shot.  Jabbing involves placing the tip of a knife at a 45° angle about 1″ from the edge of an active burrow, waiting for the larva to return to the top of the burrow, and jabbing the knife into the soil to block the larva’s retreat – a quick flip of the knife exposes the larvae, but in this case jabbing did not work because I always ended up hitting a rock and missing the larva before it ducked back down in the burrow.

Hooks on the abdominal hump of a 3rd-instar Prairie Tiger Beetle larva prevent it from being pulled out of its burrow by struggling prey.

I returned to the site where I had seen larval burrows last year and once again found them.  I tried fishing a few, though I knew this would be futile, then jabbing – again with no success, and then had an idea.  I went to the truck and retrieved a small trowel that I use to dig soil for filling rearing containers, then found an active burrow (larva sitting at the top, though dropping upon my approach) and got in position using the trowel as I would the knife.  I held the trowel firmly with both hands and placed my body behind it so I could use all my weight to force the trowel into the soil and past the rocks when the larva returned to the top of the burrow – worked like a charm!  After taking photographs of the first larva that I successfully extracted, I set to the business of collecting nearly a dozen more over the next couple of hours.  I then filled several containers with soil (using rocks in the larger one to create “compartments” to keep the larvae separated), poked “starter burrows” in the soil, and one at a time placed the extracted larvae in the burrows and sealed them in by pushing/sliding my finger over the hole.  I’ve found this is necessary to prevent the larvae from crawling right back out and digging a new burrow somewhere else – not a problem if there is only one larva in the container (although I prefer they use the starter burrows that I place at the edge of the container so that I can see them in their burrows to help keep track of what they are doing); however, in containers with more than one larva they will often encounter each other and fight, resulting in some mortality.  Larvae sealed in starter burrows eventually dig it open again but generally continue excavating it for their new burrow.  One larva was not placed in a rearing container – it was kept in a vial for the trip home, where it was dispatched and preserved in alcohol as a larval voucher specimen.

This male adult Prairie Tiger Beetle (emerged 10 weeks after collecting the larva) shows the dark olive-green coloration and semi-complete markings typical of the MO/AR disjunct population.

After returning to St. Louis, I placed the rearing containers in a growth chamber and monitored larval activity 2-3 times per week.  Whenever a burrow was opened, I would place a fall armyworm, corn earworm, or tobacco hornworm larva in the burrow and seal it shut.  Some burrows would be re-opened almost immediately and, thus, fed again, while others stayed sealed for longer periods of time.  Tap water was added to the container whenever the soil surface became quite dry – generally once per week, and by late July nearly all of the burrows were sealed and inactive. If these larvae did, indeed, represent C. obsoleta vulturina, then this would be the time they would be pupating.  On August 15 I had my answer, when I checked the containers to find the above male had emerged, and the next day two more adults emerged as well (including the female shown below).

This female adult Prairie Tiger Beetle emerged the same day as the male and shows slightly brighter green coloration.

I put the emerged adults together in the largest rearing container, and within minutes the male and one of the females were coupled. I’ve kept them fed with small caterpillars and rootworm larvae, and numerous oviposition holes were eventually observed on the surface of the soil in the container. In a few weeks, I’ll place this container in a cold incubator for the winter and then watch next spring to see if larvae hatch and begin forming burrows. If so, it will be a chance to see if I can rear the species completely from egg to adult and preserve examples of the younger larval instars.

Photo Details: Canon 50D (ISO 100, 1/250 sec) w/ Canon MT-24EX flash w/ Sto-Fen + GFPuffer diffusers. Typical post-processing (levels, minor cropping, unsharp mask).
Photos 1-2, 5-6: 100mm macro lens (f/14-f/16).
Photos 3-4: 65mm MP-E 1-5X macro lens (f/14).

Edit 9/10/10, 6:30 pm: I checked the terrarium today and discovered 24 brand new 1st-instar larval burrows dotting the soil surface.  They are quite large already, almost as big as 3rd-instar burrows of the diminutive Cylindera celeripes.  I guess I’m surprised to see larvae hatching already, as I expected they would overwinter as eggs and hatch in the spring.  Now that I think about it, however, hatching in the fall makes sense, as this gives them an opportunity to feed some before winter sets in and also allows them to burrow for more protection from freezing temperatures.  I’ve dumped a bunch of 2nd-3rd instar Lygus nymphs into the terrarium for their first meal.

Copyright © Ted C. MacRae 2010

What’s so special about this beetle?

/ Ted C. MacRae / 25 Comments

Regular readers of this blog might recognize this as the swift tiger beetle, Cylindera celeripes. This tiny, flightless beetle was once common in the central Great Plains; however, the species has experienced dramatic declines over the past century due to near complete destruction of its preferred prairie habitats.  By the time I first became interested in this species a few years ago, the Flint Hills of Kansas were its last known stronghold.

But that’s not what’s so special about this beetle.

My colleague Chris Brown and I began looking for this species as part of a survey of Missouri tiger beetles.  Although not previously known from the state, historical records from loess hilltop prairie habitats in southwestern Iowa suggested that it might be found in extreme northwestern Missouri at the southern terminus of the Loess Hills landform.  Earlier searches in this part of the state by us and others had turned up empty; however, it was easy to imagine that the beetles had eluded detection due to their small size, cryptic resemblance to ants, and limited temporal occurrence.  In an effort to understand more specifically its habitat preferences and gain a better search image for the species, we visited one of the historical Iowa localities in 2008 and succeeded in finding the species ourselves for the first time.

But that’s not what’s so special about this beetle.

Armed with this experience, Chris and I conducted another dedicated search for this species in Missouri during 2009, targeting the largest and highest quality loess hilltop prairie remnants remaining in the state.  At last, our efforts were rewarded when we found beetles in several loess hilltop prairie remnants in Atchison and Holt Counties.  Their numbers were not high at any of the sites, but the finds nevertheless represented a new state distribution for a species that has only seen contractions to its known range for many years now.

But that’s not what’s so special about this beetle.

A few weeks before finding the beetle in Missouri, I had an opportunity to visit Alabaster Caverns State Park in northwestern Oklahoma, where BugGuide contributor Charles Lewallen had photographed the species in 2003.  I not only succeeded in finding the species at the original locality but determined also that its population there was quite robust.  Indeed, on the same trip I discovered robust populations at several nearby localities, suggesting that the species occurrs commonly throughout the red clay/gypsum hills of northwestern Oklahoma.  Further observations of the species in northwestern Oklahoma last month seem to confirm this.  The beetle in these photographs comes from Alabaster Caverns, but that’s not what’s so special about it.

What is so special about it is that it’s the first ever reared individual of this species!  For those of you wondering why this is significant, until now the immature stages of this species have remained completely unknown.  A few contemporary students of the group have tried to rear the species, but the adults are delicate and do not travel well – indeed, my own first attempt to rear the species when I found it in Iowa was not successful.  However, when I found the Alabaster Caverns population, I placed ~12 adults in a small terrarium into which I had placed a chunk of native soil and moistened with water.  The adults survived well in this terrarium over several days of travel, and once back in the lab I kept them alive for several weeks by feeding them small caterpillars and fruit flies.  When larval burrows began to appear I fed them periodically with very small caterpillars and rootworm larvae, inserting them into individual burrows and sealing the burrow entrance to prevent their escape.  Additional prey larvae were inserted into burrow entrances as they were reopened, and the soil in the terrarium was moistened whenever its surface became quite dry.  By late October, all of the burrows had become inactive, and I wasn’t sure if the larvae had died or were just overwintering.  Nevertheless, I placed the terrarium in a cool (10°C) incubator, where it remained until this past March when I pulled it out of the incubator and returned it to warmer temperatures.  Within days, larval burrows reappeared, and I knew then that I had a decent chance of rearing the species to adulthood.  In early July, the beetle in these photographs emerged from its burrow – the first ever reared swift tiger beetle!  Several more adults emerged during the following 2-3 weeks.

While this rearing was in progress, I managed to find larvae of this species on a return trip to Alabaster Caverns last October.  Both 2nd- and 3rd-instar larvae were collected and preserved to go along with the preserved 1st-instar larva that I had extracted from the rearing container when larvae first began to appear.  While these preserved specimens are all that I need to complete a manuscript describing the larval instars, having reared the species completely from egg to adult as well will provide a most gratifying conclusion for that manuscript.

Copyright © Ted C. MacRae 2010

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North America’s largest tiger beetle (I think!)

/ Ted C. MacRae / 12 Comments

The generous among us might call it serendipity, while the rest of us would just call it luck.  By whatever name, I had it in spades in June last year when I made my first visit to the Glass Mountains of northwestern Oklahoma.  My original plan was to go to Tallgrass Prairie Preserve in eastern Oklahoma at the end of what proved to be a resoundingly successful day at Alabaster Caverns State Park.  However, soaking rains moved into the area and continued rumbling eastward across the plains towards the preserve, forcing a quick change of itinerary.  I decided to wait it out in the state’s western reaches, a “hunch” telling me that the red clay/gypsum hills in nearby Major County might be a fruitful place for hunting tiger beetles.  Sunny skies the next morning were a good sign, and my hunch was rewarded later that day when I discovered a previously unknown (and fortunately robust) population of the rare Cylindera celeripes (swift tiger beetle), making not just the day but the entire trip more successful than I could have ever imagined.  Icing on the cake came when I found decent numbers of the more secure but nevertheless uncommon Dromochorus pruinina (frosted dromo tiger beetle) also in the area.

Another find I made that day that I’ve mentioned on occasion but not talked about at length was a single, rather large tiger beetle larva.  I found several burrows at the base of a talus slope at the edge of a small ravine where many adult C. celeripes were scurrying, and though I tried with many, out of only one did I manage to “fish” its occupant with a blade of grass.  I didn’t know which species it represented, but its large size and occurrence in clay soil brought to mind two species – Cicindela pulchra (beautiful tiger beetle) and C. obsoleta (large grassland tiger beetle).  Both of these Great Plains species reach their eastern limit of distribution in this part of Oklahoma (Pearson et al. 2006), and their status as the largest species of the genus (and its former subgenera) in North America seemed to make them the leading candidates for this enormous larva.  There was one other possibility – Amblycheila cylindriformis (Great Plains giant tiger beetle), another Great Plains species at its eastern limit in western Oklahoma and (as the common name implies) the largest tiger beetle in all of North America.  However, to consider that species seemed too much wishful thinking.  From my understanding, larvae of that elusive species reach an incredible 45 mm in length and dig burrows  on steep slopes or at the mouths of rodent burrows that extend vertically to depths of up to 1.5 m or more (Brust et al. 2005).  Surely I could not have so casually stumbled upon such a grand grub!

I placed the larva in a terrarium of native soil and brought it back with me, and for one year now I have waited – feeding it a regular diet of the fat noctuid caterpillars that we rear so abundantly in our lab.  For a full year, I’ve watched it nab caterpillar after caterpillar, disappearing mysteriously for days on end, and just as mysteriously reappearing at the top of its burrow.  I knew getting a closer look at it would help in my attempts to determine its identity, but every time I approached with a camera it dodged down into its burrow and beat my patience.  Sometimes I would see it sitting about a centimeter below the burrow entrance – just waiting for a caterpillar to crawl by but refusing to expose itself to the lens.  I gradually decided it was likely C. pulchra, as I had seen that species in similar habitat not too far north in Barber County, Kansas.  So strong was my suspicion that I even made another trip out to the Glass Mountains in October of last year, expecting to see the fall-active adults bejeweling the exposed flats below the red clay slopes, their wine-red elytra and purple-margined bodies all aglitter under the crisp, autumn sun.  No such sight was beheld, however – my hopes dashed by the season’s sudden cold and wet turn, and with the terrarium containing the larva by then tucked away in a cool incubator for a winter’s rest, it would be several months before I would see the larva once again sitting at the top of its burrow.

In late March I pulled the terrarium out of the incubator, and within a week the larva reopened its burrow.  I fed it a few times, and then one day I saw that it had dug a new, larger  burrow – measuring a full 10 mm in diameter!  This seemed extraordinarily large for any species of Cicindela, so I resolved once again to photograph it and determine its identity.  For days I stalked it, keeping the terrarium just outside my office door where I could keep an eye on it, yet every time I approached within two feet or so it would drop down out of sight.  I decided to stop feeding it – perhaps hunger would overwhelm its patience and prompt it to return to the top of its burrow more quickly after retreating.  That seemed to work, as one day the larva came back up after only a few minutes – and I was ready!  Already  in position, I flashed off multiple shots as soon as it reappeared, moving slowly and deliberately between shots to avoid spooking it again, and managed to get a nice series from varying distances.  As a testament to its enormous size, all of the photos shown here were taken with the standard 100mm macro lens (1X maximum) – not the 65mm 1-5X beast that I needed for these shots of the super-tiny C. celeripes.

Thinking that the larva likely represented C. pulchra, I compared the photos to this photo taken by Matt Brust of a 3rd-instar larva of C. pulchra and immediately noted the differently shaped pronotum of my larva and its distinctly projecting anterolateral angles.  Compare to C. pulchra, in which the angles are in line with the median part of the anterior margin – it is clearly not that species.  It isn’t C. obsoleta either, as that species has the anterolateral angles of the pronotum even less projecting than C. pulchra (Drew and Van Cleave 1962).  Apparently I needed to rethink my assumption that it belonged to Cicindela or its close relatives – none that occur in Oklahoma are simply large enough!  Tetracha virginica is large enough, but I knew it wasn’t that species since it lacked the white margined pronotum distinctive of species in that genus (as can be seen in this post on the larva of Tetracha florida).  That left only A. cylindriformis, distinguishable from all other tiger beetle genera occurring in Oklahoma by the second (lower) pair of eyes distinctly smaller than the first (Hamilton 1925, Drew and Van Cleave 1962, Pearson et al. 2006) – clearly seen in the third photo above.  Matt Brust has also photographed the larva of A. cylindriformis – it’s not a close shot of the head and pronotum, but in general aspect my larva seems to match it well enough.

All that is left is to actually succeed in rearing this larva to adulthood.  These beasts may require up to three to four years to develop (Brust et al. 2005), although this is likely influenced by latitude and prey abundance.  I suspect it was a second instar larva when I collected it, and that it dug its new burrow this spring after molting to the third (and final) instar.  Hopefully by keeping it in a nice, warm growth chamber and feeding it generously with fat caterpillars, I can minimize the time to pupation and perhaps see the adult sometime later this summer.  If/when that happens, you can be sure to see a follow up to this post.

Photo Details: Canon 50D (ISO 100, 1/250 sec, f/16-18), Canon 100mm macro lens, Canon MT-24EX flash (1/4 ratio) w/ Sto-Fen diffusers. Post-processing: contrast and unsharp mask (no cropping).

REFERENCES:

Brust, M. L., S. M. Spomer and W. W. Hoback.  2005. Tiger Beetles of Nebraska.  University of Nebraska at Kearney.  http://www.unk.edu (Version 5APR2005).

Drew, W. A. and H. W. Van Cleave.  1962. The tiger beetles of Oklahoma (Cicindelidae).  Proceedings of the Oklahoma Academy of Science 42:101–122.

Hamilton, C. C.  1925. Studies on the morphology, taxonomy, and ecology of the larvae of Holarctic tiger beetles (family Cicindelidae).  Proceedings of the U.S. National Museum 65 (Art. 17):1–87.

Pearson, D. L., C. B. Knisley and C. J. Kazilek. 2006. A Field Guide to the Tiger Beetles of the United States and Canada. Oxford University Press, New York, 227 pp.

Copyright © Ted C. MacRae 2010

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Swift Tiger Beetle – good news, bad news

/ Ted C. MacRae / 13 Comments

Sorry about the noisy video – it was shot in one of our walk-in growth chambers with fans going full-bore! Anyway, the video shows a couple of mating pairs of Cylindera celeripes (swift tiger beetle) that I brought back from the Loess Hills of extreme northwest Missouri this past weekend.  Watch carefully and you’ll see the first pair actively copulating before they break apart. After that I pan over to the second pair, which is not actively mating but have remained coupled as an example of behavior called “mate guarding” You might also notice a few very small green “bugs” in the container – these are 2nd-instar Lygus nymphs, which I placed in the container earlier in the day as prey – it was quite a sight to see the tiger beetles immediately begin chowing down on them! At the end of the video, I poke at the second mating pair with my forefinger to give an indication of their tiny size – this flightless species is one of the smallest in all of North America! Knowing how tiny the beetles are and how well they blend into their surroundings (you’ll have to imagine the 1-2 ft of plant growth that was surrounding them in the field), you can appreciate just how difficult these beetles are to detect in their native habitat.

There is a “good news, bad news” aspect to the story behind these beetles. This rare Great Plains species was unknown from Missouri until last year, when we (Chris Brown and I) discovered it in loess hilltop prairie remnants at Brickyard Hill, Star School Hill Prairie, and McCormack Loess Mounds Conservation Areas. Loess hilltop prairie is among Missouri’s most critically endangered natural community due to its restricted occurrence at the southern tip of the Loess Hills landform and more than a century of overgrazing and relentless encroachment by woody vegetation and invasive exotics. The sites where we found the beetle last year contain the highest quality loess hilltop prairie remnants in Missouri, so we are now taking a more thorough look at some of the smaller remnants that still exist in the area. The most promising of these are at Squaw Creek National Wildlife Refuge and on several privately owned lands near the known sites, and these were the sites that I searched this past weekend. Some of these sites looked promising (one in particular looked excellent), but thorough searching at each revealed no beetles. By the time I finished searching the last of them I had begun to wonder if: 1) my “search image” for the species had gotten rusty, or 2) my timing was a bit too early (last year’s populations were discovered in late June). To test this, we (daughter Madison and I) returned to one of the known sites (McCormack) where we had seen only two beetles last year (unable to capture either one). As we hiked along the ridge top leading to the spot where we saw them, I kept a close watch on the narrow trail in front of me. Nothing. However, as soon as I came upon “the spot” I saw one! I dropped to my knees and slapped my hands down on the ground, forming an “arena” between my two thumbs and forefingers, but the beetle ran over my hand too quickly and escaped. No matter – in less than a minute I saw another one and successfully trapped it under my fingers as it ran over my other hand. During the next 15-20 minutes I would see at least eight individuals along the narrow trail in this single spot. While it was gratifying to see more individuals at this site than we had seen last year, it also meant that the timing of my searches at the other sites was fine and that I was not suffering from a rusty search image. The beetle could still be at those sites where I had failed to find it, but if it is then it certainly does not occur in very high numbers. It also bothers me that at this site the beetle seems to be restricted to one isolated ridge, which appears not to have been burned in recent years (in contrast to the rest of the preserve, which seems to have been burned within the past year or so). I searched all the remaining ridge top again thoroughly after finding the beetles again this year, but no beetles were seen anywhere except this tiny spot where we have now seen beetles in successive years.

Missouri’s few existing loess hilltop prairie remnants are not only small but highly disjunct, and the flightless nature of the beetle makes re-colonization of a remnant unlikely in the event of a localized extirpation. There is obviously much we still do not know about the impact of burning on the beetle and how best to devise management plans that consider both the habitat and the beetle. However, one thing is clear – both the habitat and the beetle are critically imperiled in Missouri, and the fate of both are in our hands, right here and right now! We’d better get this figured out quick if we’re going to save both, and there seems to be little room for error. For my part, in addition to pinpointing where our populations occur and precisely what habitats are supporting them, I am trying to develop an effective rearing technique for this never-before-reared species in the event that captive rearing becomes necessary for reintroduction or augmentation of native populations. The adults seem very delicate and do not travel well, but I have found that if I prepare a terrarium in the field for transporting the adults then they survive well – even when traveling for several days. The container measures 6 1/4” H x 8” L, and I’ve placed a chunk of native soil cut from the site where I found the beetles and kept intact. The debris on the soil surface is intact as well, but the plants growing in the soil have (obviously) been trimmed. I’ll collect eggs from these individuals and experiment with different methods that I’ve been working on for rearing the larvae to see which are the most efficient and effective.

Copyright © Ted C. MacRae 2010

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